To this point, Obama said, Russia is an "outlier" in the fight.
"We cannot succumb to fear," Obama said, standing alongside French President Francois Hollande after they met at the White House to discuss the anti-ISIS mission.
"Make no mistake, we will win, and groups like ISIL will lose."
Hollande's trip to Washington was part of a diplomatic push to get the US and other nations to bolster efforts to destroy the militant group that has claimed responsibility for the Paris attacks.
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The US and France "share the determination to fight terrorism anywhere," Hollande said, through a translator.
The French president had planned to urge Obama to work with Russia to build a new coalition to fight the extremists. But Hollande's mission quickly became entangled with the fallout from a Russian military plane downed by Turkey, an incident with echoes of the Cold War.
US forces were not involved in the air incident, according to an American military official, who was not authorized to discuss the incident publicly and so spoke on condition of anonymity.
Obama cautioned that information about the incident was still emerging and he discouraged escalation. He added that Turkey had a "right to defend its territory and its airspace."
Even before the incident between Turkey and Russia, Hollande faced a tough challenge in getting Obama to agree to a partnership with Moscow.
The US is deeply skeptical of President Vladimir Putin's motivations, given his longstanding support for Syrian President Bashar Assad.
That skepticism was clear today as both Obama and Hollande told reporters they would welcome Russia's involvement in the fight, if Moscow were to concentrate its military action on IS.